1. Field of the Invention
The present invention relates to sub-sea fibre-optic cable location apparatus.
2. Description of the Related Art
Communication systems commonly utilize sub-sea cables to carry communication signals. Due to the expanse of water separating some countries these cables often have to be extremely long and where conventional materials are used, e.g. copper, this may prove relatively expensive.
Since sub-sea cables are obscured from view and are often buried in the sea bed, the location of physical faults, for example breakage, is severely inhibited. The difficulty in locating a fault increases with the length of the sub-sea cable.
With conventional communication cables the location of breakage and the subsequent position of the broken cables may be found by using position location devices which utilise an electrical signal passed along the actual cable which either reflect or transmit signals which can be received by a cable locating apparatus. In addition, position location devices can utilise the communication cable for their source of power to transmit a position location signal.
However, the advent of fiber-optic communication cables to increase signal quality, and reduce cost with much increased carrying capacity, presents further difficulties. Even though the length of a cable before the fault may be found by injecting light into one end of the fiber and measuring the signal reflected by the fault, difficulties still occur when trying to locate the exact position of the damaged cable, particularly since the combination of ocean currents and the initial force that caused the damage may have displaced the cable a considerable distance from its original position. These difficulties arise from the fact that fiber optics do not radiate signals and the provision of conductors in the fiber-optic cable in order to power position indication transmitting devices is more difficult. Fiber-optic cables are also less detectable by conventional metal detectors because they contain less metal.
In addition, in order to protect the cable they are increasingly buried even in deep ocean beds and in these cases fiber cable location is even more difficult with conventional means.
With the increasing use of sub-sea fiber-optic cables in communication systems it would therefore be advantageous if an apparatus could be provided which locates the exact position of a fault or breakage of the cable and it is an object of the present invention to satisfy this need.